In practical terms, to actually become an MP, you would have to be selected by one of the major parties, which means you'd first have to be a member of one of those parties, and you'd have to have worked for them for a while - by financially supporting them, campaigning, supporting campaigns, being active on a local level. There is no hard and fast rule - having connections in the hierarchy of the party (whether that means, say, trade union connections, friendships from university and so on) doesn't half help, I'm betting. Not having too many skeletons in one's closet is an advantage - you might want to start clearing the really dodgy pictures off your social networking profiles and so on. Of course, you can send them to me first - I won't do anything bad with them.
Of course, actually winning the election is the final hurdle. Then you've got to be good at photo-ops, able to cut ribbons and generally waste the hard-earned money of the electorate on pointless layers of bureaucracy - and enjoy the large benefits that MPs get (hint: look for the housing allowance, you can use it to pay a mortgage on a central London property, then flog it when you get to the end of your term in office and you don't have to pay capital gains tax on the increased value of your property - and if it doesn't increase in value, you don't lose since the taxpayers paid the mortgage anyway!).